Sprague Dawley rats were born and reared under either daylight-simulating flourescent lights or high pressure sodium vapor (HPSV) lamps. The illuminances of the two lighting environments were adjusted so that the perceived brightness was the same. Rats housed under the HPSV lamps had heavier adrenals, smaller gonads (males only), larger kidneys (females only) and elevated red and white cell counts. No differences were observed between the two groups in the swim endurance, tail flick and hotplate tests.